Switching frequency in power converters (for example DC-DC buck and boost converters) is limited mainly by the ability of power transistors to manage large power with short switching times. As new process generations improve the switching quality factor, higher switching frequencies in DC-DC converters can be achieved in order to reduce the size of the passive components and increase the power efficiency. A drawback of achieving higher switching frequencies is that, as the operating frequency is increased, the current and voltage presented in the system leads to greater levels of electromagnetic interference. Electromagnetic interference (EMI) is a problem in many electronic devices and there are very strict rules as to the standards devices must meet in terms of restricting EMI to a maximum level. There are two types of EMI; conducted EMI, which enters into the power supply network from the electronic device, and radiated EMI, which is radiated into the environment of the device.
General considerations of EMI reduction in power converters are presented by Santolaria et al., in EMI Reduction in Switched Power Converters by means of Spread Spectrum Modulation Techniques, 35th Annual IEEE Power Electronics Specialists Conference, pp. 292-296, Aachen, Germany and by Feng Lin and Dan Y. Chen in Reduction of Power Supply EMI Emission by Switching Frequency Modulation, IEEE Transaction on Power Electronics, vol. 9, no. I, January 1994.
Spread spectrum clock (SSC) techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of MHz. In a DC-DC converter modulating the switching frequency using SSC techniques is becoming more and more popular with ever increasing switching frequencies. However, the use of SSC according to the prior art requires external components and/or additional silicon area.